The invention is directed to a process for the hydrolysis of 5-(.beta.-methylmercaptoethyl)-hydantoin by hydrolysis at elevated temperature and elevated pressure in an alkaline aqueous medium from which methionine can be separated.
It has long been known to obtain methionine by hydrolysis of the corresponding hydantoin.
U.S. Pat. No. 2,527,366 is directed to the hydrolysis of 5-(.beta.-methylmercaptoethyl)-hydantoin (in the following text called hydantoin (I)) in an aqueous barium hydroxide solution under pressure and elevated temperature. However, this process requires considerable amounts of expensive barium hydroxide. Experiments carried out under similar conditions with ammonium hydroxide or calcium hydroxide gave either poor yields or strongly colored products.
Furthermore, it is known from U.S. Pat. No. 2,557,920 to produce .alpha.-aminoacids by saponification of hydantoins using sodium hydroxide. According to this process, however, there are required at least 3 moles of sodium hydroxide per mole of hydantoin.
In U.S. Pat. No. 4,272,631 there is described the use of a mixture of alkali and alkaline earth hydroxides for the saponification of hydantoin (I). For the production of an alkaline methioninate solution first there must be removed by precipitation the alkaline earth ions present. Besides there are only obtained yields at a maximum of 80.5% of theory.
Employing a mixture of ammonium hydroxide and calcium hydroxide has been found completely unsatisfactory with a yield of 74%.
The process described in German AS No. 1518339 depends on the expectation that in the hydrolysis of hydantoins through removal of the gaseous reaction products ammonia and carbon dioxide the reaction equilibrium can be shifted in the direction of the formation of aminoacid and thus the yield increased.
However, to carry out the process there is required an expensive regulation of pressure which limits the pressure during the hydrolysis to a value which on the one hand is somewhat higher than the vapor pressure of water at the reaction temperature selected but on the other hand is below the theoretical autogeneously established pressure.
There has now been found a process for the hydrolysis of 5-(.beta.-methylmercaptoethyl)-hydantoin which leads to increased yields in the presence of excess ammonia.